//     Backbone.js 1.1.2

//     (c) 2010-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://backbonejs.org
define(function(require, exports, module) {

    (function (root, factory) {

        // Set up Backbone appropriately for the environment. Start with AMD.
        if (typeof define === 'function' && define.amd) {
            define(['underscore', '$', 'exports'], function (_, $, exports) {
                // Export global even in AMD case in case this script is loaded with
                // others that may still expect a global Backbone.
                root.Backbone = factory(root, exports, _, $);
            });

            // Next for Node.js or CommonJS. jQuery may not be needed as a module.
        } else if (typeof exports !== 'undefined') {
            var _ = require('underscore');
            var $ = require('$');
            factory(root, exports, _, $);

            // Finally, as a browser global.
        } else {
            root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));
        }

    }(this, function (root, Backbone, _, $) {

        // Initial Setup
        // -------------

        // Save the previous value of the `Backbone` variable, so that it can be
        // restored later on, if `noConflict` is used.
        var previousBackbone = root.Backbone;

        // Create local references to array methods we'll want to use later.
        var array = [];
        var slice = array.slice;

        // Current version of the library. Keep in sync with `package.json`.
        Backbone.VERSION = '1.1.2';

        // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
        // the `$` variable.
        Backbone.$ = $;

        // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
        // to its previous owner. Returns a reference to this Backbone object.
        Backbone.noConflict = function () {
            root.Backbone = previousBackbone;
            return this;
        };

        // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
        // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
        // set a `X-Http-Method-Override` header.
        Backbone.emulateHTTP = false;

        // Turn on `emulateJSON` to support legacy servers that can't deal with direct
        // `application/json` requests ... this will encode the body as
        // `application/x-www-form-urlencoded` instead and will send the model in a
        // form param named `model`.
        Backbone.emulateJSON = false;

        // Backbone.Events
        // ---------------

        // A module that can be mixed in to *any object* in order to provide it with
        // custom events. You may bind with `on` or remove with `off` callback
        // functions to an event; `trigger`-ing an event fires all callbacks in
        // succession.
        //
        //     var object = {};
        //     _.extend(object, Backbone.Events);
        //     object.on('expand', function(){ alert('expanded'); });
        //     object.trigger('expand');
        //
        var Events = Backbone.Events = {

            // Bind an event to a `callback` function. Passing `"all"` will bind
            // the callback to all events fired.
            on: function (name, callback, context) {
                if (!eventsApi(this, 'on', name, [callback, context]) || !callback) return this;
                this._events || (this._events = {});
                var events = this._events[name] || (this._events[name] = []);
                events.push({callback: callback, context: context, ctx: context || this});
                return this;
            },

            // Bind an event to only be triggered a single time. After the first time
            // the callback is invoked, it will be removed.
            once: function (name, callback, context) {
                if (!eventsApi(this, 'once', name, [callback, context]) || !callback) return this;
                var self = this;
                var once = _.once(function () {
                    self.off(name, once);
                    callback.apply(this, arguments);
                });
                once._callback = callback;
                return this.on(name, once, context);
            },

            // Remove one or many callbacks. If `context` is null, removes all
            // callbacks with that function. If `callback` is null, removes all
            // callbacks for the event. If `name` is null, removes all bound
            // callbacks for all events.
            off: function (name, callback, context) {
                if (!this._events || !eventsApi(this, 'off', name, [callback, context])) return this;

                // Remove all callbacks for all events.
                if (!name && !callback && !context) {
                    this._events = void 0;
                    return this;
                }

                var names = name ? [name] : _.keys(this._events);
                for (var i = 0, length = names.length; i < length; i++) {
                    name = names[i];

                    // Bail out if there are no events stored.
                    var events = this._events[name];
                    if (!events) continue;

                    // Remove all callbacks for this event.
                    if (!callback && !context) {
                        delete this._events[name];
                        continue;
                    }

                    // Find any remaining events.
                    var remaining = [];
                    for (var j = 0, k = events.length; j < k; j++) {
                        var event = events[j];
                        if (
                            callback && callback !== event.callback &&
                            callback !== event.callback._callback ||
                            context && context !== event.context
                            ) {
                            remaining.push(event);
                        }
                    }

                    // Replace events if there are any remaining.  Otherwise, clean up.
                    if (remaining.length) {
                        this._events[name] = remaining;
                    } else {
                        delete this._events[name];
                    }
                }

                return this;
            },

            // Trigger one or many events, firing all bound callbacks. Callbacks are
            // passed the same arguments as `trigger` is, apart from the event name
            // (unless you're listening on `"all"`, which will cause your callback to
            // receive the true name of the event as the first argument).
            trigger: function (name) {
                if (!this._events) return this;
                var args = slice.call(arguments, 1);
                if (!eventsApi(this, 'trigger', name, args)) return this;
                var events = this._events[name];
                var allEvents = this._events.all;
                if (events) triggerEvents(events, args);
                if (allEvents) triggerEvents(allEvents, arguments);
                return this;
            },

            // Inversion-of-control versions of `on` and `once`. Tell *this* object to
            // listen to an event in another object ... keeping track of what it's
            // listening to.
            listenTo: function (obj, name, callback) {
                var listeningTo = this._listeningTo || (this._listeningTo = {});
                var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
                listeningTo[id] = obj;
                if (!callback && typeof name === 'object') callback = this;
                obj.on(name, callback, this);
                return this;
            },

            listenToOnce: function (obj, name, callback) {
                if (typeof name === 'object') {
                    for (var event in name) this.listenToOnce(obj, event, name[event]);
                    return this;
                }
                var cb = _.once(function () {
                    this.stopListening(obj, name, cb);
                    callback.apply(this, arguments);
                });
                cb._callback = callback;
                return this.listenTo(obj, name, cb);
            },

            // Tell this object to stop listening to either specific events ... or
            // to every object it's currently listening to.
            stopListening: function (obj, name, callback) {
                var listeningTo = this._listeningTo;
                if (!listeningTo) return this;
                var remove = !name && !callback;
                if (!callback && typeof name === 'object') callback = this;
                if (obj) (listeningTo = {})[obj._listenId] = obj;
                for (var id in listeningTo) {
                    obj = listeningTo[id];
                    obj.off(name, callback, this);
                    if (remove || _.isEmpty(obj._events)) delete this._listeningTo[id];
                }
                return this;
            }

        };

        // Regular expression used to split event strings.
        var eventSplitter = /\s+/;

        // Implement fancy features of the Events API such as multiple event
        // names `"change blur"` and jQuery-style event maps `{change: action}`
        // in terms of the existing API.
        var eventsApi = function (obj, action, name, rest) {
            if (!name) return true;

            // Handle event maps.
            if (typeof name === 'object') {
                for (var key in name) {
                    obj[action].apply(obj, [key, name[key]].concat(rest));
                }
                return false;
            }

            // Handle space separated event names.
            if (eventSplitter.test(name)) {
                var names = name.split(eventSplitter);
                for (var i = 0, length = names.length; i < length; i++) {
                    obj[action].apply(obj, [names[i]].concat(rest));
                }
                return false;
            }

            return true;
        };

        // A difficult-to-believe, but optimized internal dispatch function for
        // triggering events. Tries to keep the usual cases speedy (most internal
        // Backbone events have 3 arguments).
        var triggerEvents = function (events, args) {
            var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
            switch (args.length) {
                case 0:
                    while (++i < l) (ev = events[i]).callback.call(ev.ctx);
                    return;
                case 1:
                    while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1);
                    return;
                case 2:
                    while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2);
                    return;
                case 3:
                    while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3);
                    return;
                default:
                    while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args);
                    return;
            }
        };

        // Aliases for backwards compatibility.
        Events.bind = Events.on;
        Events.unbind = Events.off;

        // Allow the `Backbone` object to serve as a global event bus, for folks who
        // want global "pubsub" in a convenient place.
        _.extend(Backbone, Events);

        // Backbone.Model
        // --------------

        // Backbone **Models** are the basic data object in the framework --
        // frequently representing a row in a table in a database on your server.
        // A discrete chunk of data and a bunch of useful, related methods for
        // performing computations and transformations on that data.

        // Create a new model with the specified attributes. A client id (`cid`)
        // is automatically generated and assigned for you.
        var Model = Backbone.Model = function (attributes, options) {
            var attrs = attributes || {};
            options || (options = {});
            this.cid = _.uniqueId('c');
            this.attributes = {};
            if (options.collection) this.collection = options.collection;
            if (options.parse) attrs = this.parse(attrs, options) || {};
            attrs = _.defaults({}, attrs, _.result(this, 'defaults'));
            this.set(attrs, options);
            this.changed = {};
            this.initialize.apply(this, arguments);
        };

        // Attach all inheritable methods to the Model prototype.
        _.extend(Model.prototype, Events, {

            // A hash of attributes whose current and previous value differ.
            changed: null,

            // The value returned during the last failed validation.
            validationError: null,

            // The default name for the JSON `id` attribute is `"id"`. MongoDB and
            // CouchDB users may want to set this to `"_id"`.
            idAttribute: 'id',

            // Initialize is an empty function by default. Override it with your own
            // initialization logic.
            initialize: function () {
            },

            // Return a copy of the model's `attributes` object.
            toJSON: function (options) {
                return _.clone(this.attributes);
            },

            // Proxy `Backbone.sync` by default -- but override this if you need
            // custom syncing semantics for *this* particular model.
            sync: function () {
                return Backbone.sync.apply(this, arguments);
            },

            // Get the value of an attribute.
            get: function (attr) {
                return this.attributes[attr];
            },

            // Get the HTML-escaped value of an attribute.
            escape: function (attr) {
                return _.escape(this.get(attr));
            },

            // Returns `true` if the attribute contains a value that is not null
            // or undefined.
            has: function (attr) {
                return this.get(attr) != null;
            },

            // Special-cased proxy to underscore's `_.matches` method.
            matches: function (attrs) {
                return _.matches(attrs)(this.attributes);
            },

            // Set a hash of model attributes on the object, firing `"change"`. This is
            // the core primitive operation of a model, updating the data and notifying
            // anyone who needs to know about the change in state. The heart of the beast.
            set: function (key, val, options) {
                var attr, attrs, unset, changes, silent, changing, prev, current;
                if (key == null) return this;

                // Handle both `"key", value` and `{key: value}` -style arguments.
                if (typeof key === 'object') {
                    attrs = key;
                    options = val;
                } else {
                    (attrs = {})[key] = val;
                }

                options || (options = {});

                // Run validation.
                if (!this._validate(attrs, options)) return false;

                // Extract attributes and options.
                unset = options.unset;
                silent = options.silent;
                changes = [];
                changing = this._changing;
                this._changing = true;

                if (!changing) {
                    this._previousAttributes = _.clone(this.attributes);
                    this.changed = {};
                }
                current = this.attributes, prev = this._previousAttributes;

                // Check for changes of `id`.
                if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];

                // For each `set` attribute, update or delete the current value.
                for (attr in attrs) {
                    val = attrs[attr];
                    if (!_.isEqual(current[attr], val)) changes.push(attr);
                    if (!_.isEqual(prev[attr], val)) {
                        this.changed[attr] = val;
                    } else {
                        delete this.changed[attr];
                    }
                    unset ? delete current[attr] : current[attr] = val;
                }

                // Trigger all relevant attribute changes.
                if (!silent) {
                    if (changes.length) this._pending = options;
                    for (var i = 0, length = changes.length; i < length; i++) {
                        this.trigger('change:' + changes[i], this, current[changes[i]], options);
                    }
                }

                // You might be wondering why there's a `while` loop here. Changes can
                // be recursively nested within `"change"` events.
                if (changing) return this;
                if (!silent) {
                    while (this._pending) {
                        options = this._pending;
                        this._pending = false;
                        this.trigger('change', this, options);
                    }
                }
                this._pending = false;
                this._changing = false;
                return this;
            },

            // Remove an attribute from the model, firing `"change"`. `unset` is a noop
            // if the attribute doesn't exist.
            unset: function (attr, options) {
                return this.set(attr, void 0, _.extend({}, options, {unset: true}));
            },

            // Clear all attributes on the model, firing `"change"`.
            clear: function (options) {
                var attrs = {};
                for (var key in this.attributes) attrs[key] = void 0;
                return this.set(attrs, _.extend({}, options, {unset: true}));
            },

            // Determine if the model has changed since the last `"change"` event.
            // If you specify an attribute name, determine if that attribute has changed.
            hasChanged: function (attr) {
                if (attr == null) return !_.isEmpty(this.changed);
                return _.has(this.changed, attr);
            },

            // Return an object containing all the attributes that have changed, or
            // false if there are no changed attributes. Useful for determining what
            // parts of a view need to be updated and/or what attributes need to be
            // persisted to the server. Unset attributes will be set to undefined.
            // You can also pass an attributes object to diff against the model,
            // determining if there *would be* a change.
            changedAttributes: function (diff) {
                if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
                var val, changed = false;
                var old = this._changing ? this._previousAttributes : this.attributes;
                for (var attr in diff) {
                    if (_.isEqual(old[attr], (val = diff[attr]))) continue;
                    (changed || (changed = {}))[attr] = val;
                }
                return changed;
            },

            // Get the previous value of an attribute, recorded at the time the last
            // `"change"` event was fired.
            previous: function (attr) {
                if (attr == null || !this._previousAttributes) return null;
                return this._previousAttributes[attr];
            },

            // Get all of the attributes of the model at the time of the previous
            // `"change"` event.
            previousAttributes: function () {
                return _.clone(this._previousAttributes);
            },

            // Fetch the model from the server. If the server's representation of the
            // model differs from its current attributes, they will be overridden,
            // triggering a `"change"` event.
            fetch: function (options) {
                options = options ? _.clone(options) : {};
                if (options.parse === void 0) options.parse = true;
                var model = this;
                var success = options.success;
                options.success = function (resp) {
                    if (!model.set(model.parse(resp, options), options)) return false;
                    if (success) success(model, resp, options);
                    model.trigger('sync', model, resp, options);
                };
                wrapError(this, options);
                return this.sync('read', this, options);
            },

            // Set a hash of model attributes, and sync the model to the server.
            // If the server returns an attributes hash that differs, the model's
            // state will be `set` again.
            save: function (key, val, options) {
                var attrs, method, xhr, attributes = this.attributes;

                // Handle both `"key", value` and `{key: value}` -style arguments.
                if (key == null || typeof key === 'object') {
                    attrs = key;
                    options = val;
                } else {
                    (attrs = {})[key] = val;
                }

                options = _.extend({validate: true}, options);

                // If we're not waiting and attributes exist, save acts as
                // `set(attr).save(null, opts)` with validation. Otherwise, check if
                // the model will be valid when the attributes, if any, are set.
                if (attrs && !options.wait) {
                    if (!this.set(attrs, options)) return false;
                } else {
                    if (!this._validate(attrs, options)) return false;
                }

                // Set temporary attributes if `{wait: true}`.
                if (attrs && options.wait) {
                    this.attributes = _.extend({}, attributes, attrs);
                }

                // After a successful server-side save, the client is (optionally)
                // updated with the server-side state.
                if (options.parse === void 0) options.parse = true;
                var model = this;
                var success = options.success;
                options.success = function (resp) {
                    // Ensure attributes are restored during synchronous saves.
                    model.attributes = attributes;
                    var serverAttrs = model.parse(resp, options);
                    if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
                    if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {
                        return false;
                    }
                    if (success) success(model, resp, options);
                    model.trigger('sync', model, resp, options);
                };
                wrapError(this, options);

                method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
                if (method === 'patch' && !options.attrs) options.attrs = attrs;
                xhr = this.sync(method, this, options);

                // Restore attributes.
                if (attrs && options.wait) this.attributes = attributes;

                return xhr;
            },

            // Destroy this model on the server if it was already persisted.
            // Optimistically removes the model from its collection, if it has one.
            // If `wait: true` is passed, waits for the server to respond before removal.
            destroy: function (options) {
                options = options ? _.clone(options) : {};
                var model = this;
                var success = options.success;

                var destroy = function () {
                    model.stopListening();
                    model.trigger('destroy', model, model.collection, options);
                };

                options.success = function (resp) {
                    if (options.wait || model.isNew()) destroy();
                    if (success) success(model, resp, options);
                    if (!model.isNew()) model.trigger('sync', model, resp, options);
                };

                if (this.isNew()) {
                    options.success();
                    return false;
                }
                wrapError(this, options);

                var xhr = this.sync('delete', this, options);
                if (!options.wait) destroy();
                return xhr;
            },

            // Default URL for the model's representation on the server -- if you're
            // using Backbone's restful methods, override this to change the endpoint
            // that will be called.
            url: function () {
                var base =
                    _.result(this, 'urlRoot') ||
                    _.result(this.collection, 'url') ||
                    urlError();
                if (this.isNew()) return base;
                return base.replace(/([^\/])$/, '$1/') + encodeURIComponent(this.id);
            },

            // **parse** converts a response into the hash of attributes to be `set` on
            // the model. The default implementation is just to pass the response along.
            parse: function (resp, options) {
                return resp;
            },

            // Create a new model with identical attributes to this one.
            clone: function () {
                return new this.constructor(this.attributes);
            },

            // A model is new if it has never been saved to the server, and lacks an id.
            isNew: function () {
                return !this.has(this.idAttribute);
            },

            // Check if the model is currently in a valid state.
            isValid: function (options) {
                return this._validate({}, _.extend(options || {}, { validate: true }));
            },

            // Run validation against the next complete set of model attributes,
            // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
            _validate: function (attrs, options) {
                if (!options.validate || !this.validate) return true;
                attrs = _.extend({}, this.attributes, attrs);
                var error = this.validationError = this.validate(attrs, options) || null;
                if (!error) return true;
                this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
                return false;
            }

        });

        // Underscore methods that we want to implement on the Model.
        var modelMethods = ['keys', 'values', 'pairs', 'invert', 'pick', 'omit', 'chain', 'isEmpty'];

        // Mix in each Underscore method as a proxy to `Model#attributes`.
        _.each(modelMethods, function (method) {
            if (!_[method]) return;
            Model.prototype[method] = function () {
                var args = slice.call(arguments);
                args.unshift(this.attributes);
                return _[method].apply(_, args);
            };
        });

        // Backbone.Collection
        // -------------------

        // If models tend to represent a single row of data, a Backbone Collection is
        // more analogous to a table full of data ... or a small slice or page of that
        // table, or a collection of rows that belong together for a particular reason
        // -- all of the messages in this particular folder, all of the documents
        // belonging to this particular author, and so on. Collections maintain
        // indexes of their models, both in order, and for lookup by `id`.

        // Create a new **Collection**, perhaps to contain a specific type of `model`.
        // If a `comparator` is specified, the Collection will maintain
        // its models in sort order, as they're added and removed.
        var Collection = Backbone.Collection = function (models, options) {
            options || (options = {});
            if (options.model) this.model = options.model;
            if (options.comparator !== void 0) this.comparator = options.comparator;
            this._reset();
            this.initialize.apply(this, arguments);
            if (models) this.reset(models, _.extend({silent: true}, options));
        };

        // Default options for `Collection#set`.
        var setOptions = {add: true, remove: true, merge: true};
        var addOptions = {add: true, remove: false};

        // Define the Collection's inheritable methods.
        _.extend(Collection.prototype, Events, {

            // The default model for a collection is just a **Backbone.Model**.
            // This should be overridden in most cases.
            model: Model,

            // Initialize is an empty function by default. Override it with your own
            // initialization logic.
            initialize: function () {
            },

            // The JSON representation of a Collection is an array of the
            // models' attributes.
            toJSON: function (options) {
                return this.map(function (model) {
                    return model.toJSON(options);
                });
            },

            // Proxy `Backbone.sync` by default.
            sync: function () {
                return Backbone.sync.apply(this, arguments);
            },

            // Add a model, or list of models to the set.
            add: function (models, options) {
                return this.set(models, _.extend({merge: false}, options, addOptions));
            },

            // Remove a model, or a list of models from the set.
            remove: function (models, options) {
                var singular = !_.isArray(models);
                models = singular ? [models] : _.clone(models);
                options || (options = {});
                for (var i = 0, length = models.length; i < length; i++) {
                    var model = models[i] = this.get(models[i]);
                    if (!model) continue;
                    var id = this.modelId(model.attributes);
                    if (id != null) delete this._byId[id];
                    delete this._byId[model.cid];
                    var index = this.indexOf(model);
                    this.models.splice(index, 1);
                    this.length--;
                    if (!options.silent) {
                        options.index = index;
                        model.trigger('remove', model, this, options);
                    }
                    this._removeReference(model, options);
                }
                return singular ? models[0] : models;
            },

            // Update a collection by `set`-ing a new list of models, adding new ones,
            // removing models that are no longer present, and merging models that
            // already exist in the collection, as necessary. Similar to **Model#set**,
            // the core operation for updating the data contained by the collection.
            set: function (models, options) {
                options = _.defaults({}, options, setOptions);
                if (options.parse) models = this.parse(models, options);
                var singular = !_.isArray(models);
                models = singular ? (models ? [models] : []) : models.slice();
                var id, model, attrs, existing, sort;
                var at = options.at;
                if (at < 0) at += this.length + 1;
                var sortable = this.comparator && (at == null) && options.sort !== false;
                var sortAttr = _.isString(this.comparator) ? this.comparator : null;
                var toAdd = [], toRemove = [], modelMap = {};
                var add = options.add, merge = options.merge, remove = options.remove;
                var order = !sortable && add && remove ? [] : false;
                var orderChanged = false;

                // Turn bare objects into model references, and prevent invalid models
                // from being added.
                for (var i = 0, length = models.length; i < length; i++) {
                    attrs = models[i];

                    // If a duplicate is found, prevent it from being added and
                    // optionally merge it into the existing model.
                    if (existing = this.get(attrs)) {
                        if (remove) modelMap[existing.cid] = true;
                        if (merge && attrs !== existing) {
                            attrs = this._isModel(attrs) ? attrs.attributes : attrs;
                            if (options.parse) attrs = existing.parse(attrs, options);
                            existing.set(attrs, options);
                            if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
                        }
                        models[i] = existing;

                        // If this is a new, valid model, push it to the `toAdd` list.
                    } else if (add) {
                        model = models[i] = this._prepareModel(attrs, options);
                        if (!model) continue;
                        toAdd.push(model);
                        this._addReference(model, options);
                    }

                    // Do not add multiple models with the same `id`.
                    model = existing || model;
                    if (!model) continue;
                    id = this.modelId(model.attributes);
                    if (order && (model.isNew() || !modelMap[id])) {
                        order.push(model);

                        // Check to see if this is actually a new model at this index.
                        orderChanged = orderChanged || !this.models[i] || model.cid !== this.models[i].cid;
                    }

                    modelMap[id] = true;
                }

                // Remove nonexistent models if appropriate.
                if (remove) {
                    for (var i = 0, length = this.length; i < length; i++) {
                        if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
                    }
                    if (toRemove.length) this.remove(toRemove, options);
                }

                // See if sorting is needed, update `length` and splice in new models.
                if (toAdd.length || orderChanged) {
                    if (sortable) sort = true;
                    this.length += toAdd.length;
                    if (at != null) {
                        for (var i = 0, length = toAdd.length; i < length; i++) {
                            this.models.splice(at + i, 0, toAdd[i]);
                        }
                    } else {
                        if (order) this.models.length = 0;
                        var orderedModels = order || toAdd;
                        for (var i = 0, length = orderedModels.length; i < length; i++) {
                            this.models.push(orderedModels[i]);
                        }
                    }
                }

                // Silently sort the collection if appropriate.
                if (sort) this.sort({silent: true});

                // Unless silenced, it's time to fire all appropriate add/sort events.
                if (!options.silent) {
                    var addOpts = at != null ? _.clone(options) : options;
                    for (var i = 0, length = toAdd.length; i < length; i++) {
                        if (at != null) addOpts.index = at + i;
                        (model = toAdd[i]).trigger('add', model, this, addOpts);
                    }
                    if (sort || orderChanged) this.trigger('sort', this, options);
                }

                // Return the added (or merged) model (or models).
                return singular ? models[0] : models;
            },

            // When you have more items than you want to add or remove individually,
            // you can reset the entire set with a new list of models, without firing
            // any granular `add` or `remove` events. Fires `reset` when finished.
            // Useful for bulk operations and optimizations.
            reset: function (models, options) {
                options = options ? _.clone(options) : {};
                for (var i = 0, length = this.models.length; i < length; i++) {
                    this._removeReference(this.models[i], options);
                }
                options.previousModels = this.models;
                this._reset();
                models = this.add(models, _.extend({silent: true}, options));
                if (!options.silent) this.trigger('reset', this, options);
                return models;
            },

            // Add a model to the end of the collection.
            push: function (model, options) {
                return this.add(model, _.extend({at: this.length}, options));
            },

            // Remove a model from the end of the collection.
            pop: function (options) {
                var model = this.at(this.length - 1);
                this.remove(model, options);
                return model;
            },

            // Add a model to the beginning of the collection.
            unshift: function (model, options) {
                return this.add(model, _.extend({at: 0}, options));
            },

            // Remove a model from the beginning of the collection.
            shift: function (options) {
                var model = this.at(0);
                this.remove(model, options);
                return model;
            },

            // Slice out a sub-array of models from the collection.
            slice: function () {
                return slice.apply(this.models, arguments);
            },

            // Get a model from the set by id.
            get: function (obj) {
                if (obj == null) return void 0;
                var id = this.modelId(this._isModel(obj) ? obj.attributes : obj);
                return this._byId[obj] || this._byId[id] || this._byId[obj.cid];
            },

            // Get the model at the given index.
            at: function (index) {
                if (index < 0) index += this.length;
                return this.models[index];
            },

            // Return models with matching attributes. Useful for simple cases of
            // `filter`.
            where: function (attrs, first) {
                var matches = _.matches(attrs);
                return this[first ? 'find' : 'filter'](function (model) {
                    return matches(model.attributes);
                });
            },

            // Return the first model with matching attributes. Useful for simple cases
            // of `find`.
            findWhere: function (attrs) {
                return this.where(attrs, true);
            },

            // Force the collection to re-sort itself. You don't need to call this under
            // normal circumstances, as the set will maintain sort order as each item
            // is added.
            sort: function (options) {
                if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
                options || (options = {});

                // Run sort based on type of `comparator`.
                if (_.isString(this.comparator) || this.comparator.length === 1) {
                    this.models = this.sortBy(this.comparator, this);
                } else {
                    this.models.sort(_.bind(this.comparator, this));
                }

                if (!options.silent) this.trigger('sort', this, options);
                return this;
            },

            // Pluck an attribute from each model in the collection.
            pluck: function (attr) {
                return _.invoke(this.models, 'get', attr);
            },

            // Fetch the default set of models for this collection, resetting the
            // collection when they arrive. If `reset: true` is passed, the response
            // data will be passed through the `reset` method instead of `set`.
            fetch: function (options) {
                options = options ? _.clone(options) : {};
                if (options.parse === void 0) options.parse = true;
                var success = options.success;
                var collection = this;
                options.success = function (resp) {
                    var method = options.reset ? 'reset' : 'set';
                    collection[method](resp, options);
                    if (success) success(collection, resp, options);
                    collection.trigger('sync', collection, resp, options);
                };
                wrapError(this, options);
                return this.sync('read', this, options);
            },

            // Create a new instance of a model in this collection. Add the model to the
            // collection immediately, unless `wait: true` is passed, in which case we
            // wait for the server to agree.
            create: function (model, options) {
                options = options ? _.clone(options) : {};
                if (!(model = this._prepareModel(model, options))) return false;
                if (!options.wait) this.add(model, options);
                var collection = this;
                var success = options.success;
                options.success = function (model, resp) {
                    if (options.wait) collection.add(model, options);
                    if (success) success(model, resp, options);
                };
                model.save(null, options);
                return model;
            },

            // **parse** converts a response into a list of models to be added to the
            // collection. The default implementation is just to pass it through.
            parse: function (resp, options) {
                return resp;
            },

            // Create a new collection with an identical list of models as this one.
            clone: function () {
                return new this.constructor(this.models, {
                    model: this.model,
                    comparator: this.comparator
                });
            },

            // Define how to uniquely identify models in the collection.
            modelId: function (attrs) {
                return attrs[this.model.prototype.idAttribute || 'id'];
            },

            // Private method to reset all internal state. Called when the collection
            // is first initialized or reset.
            _reset: function () {
                this.length = 0;
                this.models = [];
                this._byId = {};
            },

            // Prepare a hash of attributes (or other model) to be added to this
            // collection.
            _prepareModel: function (attrs, options) {
                if (this._isModel(attrs)) {
                    if (!attrs.collection) attrs.collection = this;
                    return attrs;
                }
                options = options ? _.clone(options) : {};
                options.collection = this;
                var model = new this.model(attrs, options);
                if (!model.validationError) return model;
                this.trigger('invalid', this, model.validationError, options);
                return false;
            },

            // Method for checking whether an object should be considered a model for
            // the purposes of adding to the collection.
            _isModel: function (model) {
                return model instanceof Model;
            },

            // Internal method to create a model's ties to a collection.
            _addReference: function (model, options) {
                this._byId[model.cid] = model;
                var id = this.modelId(model.attributes);
                if (id != null) this._byId[id] = model;
                model.on('all', this._onModelEvent, this);
            },

            // Internal method to sever a model's ties to a collection.
            _removeReference: function (model, options) {
                if (this === model.collection) delete model.collection;
                model.off('all', this._onModelEvent, this);
            },

            // Internal method called every time a model in the set fires an event.
            // Sets need to update their indexes when models change ids. All other
            // events simply proxy through. "add" and "remove" events that originate
            // in other collections are ignored.
            _onModelEvent: function (event, model, collection, options) {
                if ((event === 'add' || event === 'remove') && collection !== this) return;
                if (event === 'destroy') this.remove(model, options);
                if (event === 'change') {
                    var prevId = this.modelId(model.previousAttributes());
                    var id = this.modelId(model.attributes);
                    if (prevId !== id) {
                        if (prevId != null) delete this._byId[prevId];
                        if (id != null) this._byId[id] = model;
                    }
                }
                this.trigger.apply(this, arguments);
            }

        });

        // Underscore methods that we want to implement on the Collection.
        // 90% of the core usefulness of Backbone Collections is actually implemented
        // right here:
        var methods = ['forEach', 'each', 'map', 'collect', 'reduce', 'foldl',
            'inject', 'reduceRight', 'foldr', 'find', 'detect', 'filter', 'select',
            'reject', 'every', 'all', 'some', 'any', 'include', 'contains', 'invoke',
            'max', 'min', 'toArray', 'size', 'first', 'head', 'take', 'initial', 'rest',
            'tail', 'drop', 'last', 'without', 'difference', 'indexOf', 'shuffle',
            'lastIndexOf', 'isEmpty', 'chain', 'sample', 'partition'];

        // Mix in each Underscore method as a proxy to `Collection#models`.
        _.each(methods, function (method) {
            if (!_[method]) return;
            Collection.prototype[method] = function () {
                var args = slice.call(arguments);
                args.unshift(this.models);
                return _[method].apply(_, args);
            };
        });

        // Underscore methods that take a property name as an argument.
        var attributeMethods = ['groupBy', 'countBy', 'sortBy', 'indexBy'];

        // Use attributes instead of properties.
        _.each(attributeMethods, function (method) {
            if (!_[method]) return;
            Collection.prototype[method] = function (value, context) {
                var iterator = _.isFunction(value) ? value : function (model) {
                    return model.get(value);
                };
                return _[method](this.models, iterator, context);
            };
        });

        // Backbone.View
        // -------------

        // Backbone Views are almost more convention than they are actual code. A View
        // is simply a JavaScript object that represents a logical chunk of UI in the
        // DOM. This might be a single item, an entire list, a sidebar or panel, or
        // even the surrounding frame which wraps your whole app. Defining a chunk of
        // UI as a **View** allows you to define your DOM events declaratively, without
        // having to worry about render order ... and makes it easy for the view to
        // react to specific changes in the state of your models.

        // Creating a Backbone.View creates its initial element outside of the DOM,
        // if an existing element is not provided...
        var View = Backbone.View = function (options) {
            this.cid = _.uniqueId('view');
            options || (options = {});
            _.extend(this, _.pick(options, viewOptions));
            this._ensureElement();
            this.initialize.apply(this, arguments);
        };

        // Cached regex to split keys for `delegate`.
        var delegateEventSplitter = /^(\S+)\s*(.*)$/;

        // List of view options to be merged as properties.
        var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];

        // Set up all inheritable **Backbone.View** properties and methods.
        _.extend(View.prototype, Events, {

            // The default `tagName` of a View's element is `"div"`.
            tagName: 'div',

            // jQuery delegate for element lookup, scoped to DOM elements within the
            // current view. This should be preferred to global lookups where possible.
            $: function (selector) {
                return this.$el.find(selector);
            },

            // Initialize is an empty function by default. Override it with your own
            // initialization logic.
            initialize: function () {
            },

            // **render** is the core function that your view should override, in order
            // to populate its element (`this.el`), with the appropriate HTML. The
            // convention is for **render** to always return `this`.
            render: function () {
                return this;
            },

            // Remove this view by taking the element out of the DOM, and removing any
            // applicable Backbone.Events listeners.
            remove: function () {
                this._removeElement();
                this.stopListening();
                return this;
            },

            // Remove this view's element from the document and all event listeners
            // attached to it. Exposed for subclasses using an alternative DOM
            // manipulation API.
            _removeElement: function () {
                this.$el.remove();
            },

            // Change the view's element (`this.el` property) and re-delegate the
            // view's events on the new element.
            setElement: function (element) {
                this.undelegateEvents();
                this._setElement(element);
                this.delegateEvents();
                return this;
            },

            // Creates the `this.el` and `this.$el` references for this view using the
            // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
            // context or an element. Subclasses can override this to utilize an
            // alternative DOM manipulation API and are only required to set the
            // `this.el` property.
            _setElement: function (el) {
                this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
                this.el = this.$el[0];
            },

            // Set callbacks, where `this.events` is a hash of
            //
            // *{"event selector": "callback"}*
            //
            //     {
            //       'mousedown .title':  'edit',
            //       'click .button':     'save',
            //       'click .open':       function(e) { ... }
            //     }
            //
            // pairs. Callbacks will be bound to the view, with `this` set properly.
            // Uses event delegation for efficiency.
            // Omitting the selector binds the event to `this.el`.
            delegateEvents: function (events) {
                if (!(events || (events = _.result(this, 'events')))) return this;
                this.undelegateEvents();
                for (var key in events) {
                    var method = events[key];
                    if (!_.isFunction(method)) method = this[events[key]];
                    if (!method) continue;
                    var match = key.match(delegateEventSplitter);
                    this.delegate(match[1], match[2], _.bind(method, this));
                }
                return this;
            },

            // Add a single event listener to the view's element (or a child element
            // using `selector`). This only works for delegate-able events: not `focus`,
            // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
            delegate: function (eventName, selector, listener) {
                this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
            },

            // Clears all callbacks previously bound to the view by `delegateEvents`.
            // You usually don't need to use this, but may wish to if you have multiple
            // Backbone views attached to the same DOM element.
            undelegateEvents: function () {
                if (this.$el) this.$el.off('.delegateEvents' + this.cid);
                return this;
            },

            // A finer-grained `undelegateEvents` for removing a single delegated event.
            // `selector` and `listener` are both optional.
            undelegate: function (eventName, selector, listener) {
                this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
            },

            // Produces a DOM element to be assigned to your view. Exposed for
            // subclasses using an alternative DOM manipulation API.
            _createElement: function (tagName) {
                return document.createElement(tagName);
            },

            // Ensure that the View has a DOM element to render into.
            // If `this.el` is a string, pass it through `$()`, take the first
            // matching element, and re-assign it to `el`. Otherwise, create
            // an element from the `id`, `className` and `tagName` properties.
            _ensureElement: function () {
                if (!this.el) {
                    var attrs = _.extend({}, _.result(this, 'attributes'));
                    if (this.id) attrs.id = _.result(this, 'id');
                    if (this.className) attrs['class'] = _.result(this, 'className');
                    this.setElement(this._createElement(_.result(this, 'tagName')));
                    this._setAttributes(attrs);
                } else {
                    this.setElement(_.result(this, 'el'));
                }
            },

            // Set attributes from a hash on this view's element.  Exposed for
            // subclasses using an alternative DOM manipulation API.
            _setAttributes: function (attributes) {
                this.$el.attr(attributes);
            }

        });

        // Backbone.sync
        // -------------

        // Override this function to change the manner in which Backbone persists
        // models to the server. You will be passed the type of request, and the
        // model in question. By default, makes a RESTful Ajax request
        // to the model's `url()`. Some possible customizations could be:
        //
        // * Use `setTimeout` to batch rapid-fire updates into a single request.
        // * Send up the models as XML instead of JSON.
        // * Persist models via WebSockets instead of Ajax.
        //
        // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
        // as `POST`, with a `_method` parameter containing the true HTTP method,
        // as well as all requests with the body as `application/x-www-form-urlencoded`
        // instead of `application/json` with the model in a param named `model`.
        // Useful when interfacing with server-side languages like **PHP** that make
        // it difficult to read the body of `PUT` requests.
        Backbone.sync = function (method, model, options) {
            var type = methodMap[method];

            // Default options, unless specified.
            _.defaults(options || (options = {}), {
                emulateHTTP: Backbone.emulateHTTP,
                emulateJSON: Backbone.emulateJSON
            });

            // Default JSON-request options.
            var params = {type: type, dataType: 'json'};

            // Ensure that we have a URL.
            if (!options.url) {
                params.url = _.result(model, 'url') || urlError();
            }

            // Ensure that we have the appropriate request data.
            if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
                params.contentType = 'application/json';
                params.data = JSON.stringify(options.attrs || model.toJSON(options));
            }

            // For older servers, emulate JSON by encoding the request into an HTML-form.
            if (options.emulateJSON) {
                params.contentType = 'application/x-www-form-urlencoded';
                params.data = params.data ? {model: params.data} : {};
            }

            // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
            // And an `X-HTTP-Method-Override` header.
            if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
                params.type = 'POST';
                if (options.emulateJSON) params.data._method = type;
                var beforeSend = options.beforeSend;
                options.beforeSend = function (xhr) {
                    xhr.setRequestHeader('X-HTTP-Method-Override', type);
                    if (beforeSend) return beforeSend.apply(this, arguments);
                };
            }

            // Don't process data on a non-GET request.
            if (params.type !== 'GET' && !options.emulateJSON) {
                params.processData = false;
            }

            // Pass along `textStatus` and `errorThrown` from jQuery.
            var error = options.error;
            options.error = function (xhr, textStatus, errorThrown) {
                options.textStatus = textStatus;
                options.errorThrown = errorThrown;
                if (error) error.apply(this, arguments);
            };

            // Make the request, allowing the user to override any Ajax options.
            var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
            model.trigger('request', model, xhr, options);
            return xhr;
        };

        // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
        var methodMap = {
            'create': 'POST',
            'update': 'PUT',
            'patch': 'PATCH',
            'delete': 'DELETE',
            'read': 'GET'
        };

        // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
        // Override this if you'd like to use a different library.
        Backbone.ajax = function () {
            return Backbone.$.ajax.apply(Backbone.$, arguments);
        };

        // Backbone.Router
        // ---------------

        // Routers map faux-URLs to actions, and fire events when routes are
        // matched. Creating a new one sets its `routes` hash, if not set statically.
        var Router = Backbone.Router = function (options) {
            options || (options = {});
            if (options.routes) this.routes = options.routes;
            this._bindRoutes();
            this.initialize.apply(this, arguments);
        };

        // Cached regular expressions for matching named param parts and splatted
        // parts of route strings.
        var optionalParam = /\((.*?)\)/g;
        var namedParam = /(\(\?)?:\w+/g;
        var splatParam = /\*\w+/g;
        var escapeRegExp = /[\-{}\[\]+?.,\\\^$|#\s]/g;

        // Set up all inheritable **Backbone.Router** properties and methods.
        _.extend(Router.prototype, Events, {

            // Initialize is an empty function by default. Override it with your own
            // initialization logic.
            initialize: function () {
            },

            // Manually bind a single named route to a callback. For example:
            //
            //     this.route('search/:query/p:num', 'search', function(query, num) {
            //       ...
            //     });
            //
            route: function (route, name, callback) {
                if (!_.isRegExp(route)) route = this._routeToRegExp(route);
                if (_.isFunction(name)) {
                    callback = name;
                    name = '';
                }
                if (!callback) callback = this[name];
                var router = this;
                Backbone.history.route(route, function (fragment) {
                    var args = router._extractParameters(route, fragment);
                    if (router.execute(callback, args, name) !== false) {
                        router.trigger.apply(router, ['route:' + name].concat(args));
                        router.trigger('route', name, args);
                        Backbone.history.trigger('route', router, name, args);
                    }
                });
                return this;
            },

            // Execute a route handler with the provided parameters.  This is an
            // excellent place to do pre-route setup or post-route cleanup.
            execute: function (callback, args, name) {
                if (callback) callback.apply(this, args);
            },

            // Simple proxy to `Backbone.history` to save a fragment into the history.
            navigate: function (fragment, options) {
                Backbone.history.navigate(fragment, options);
                return this;
            },

            // Bind all defined routes to `Backbone.history`. We have to reverse the
            // order of the routes here to support behavior where the most general
            // routes can be defined at the bottom of the route map.
            _bindRoutes: function () {
                if (!this.routes) return;
                this.routes = _.result(this, 'routes');
                var route, routes = _.keys(this.routes);
                while ((route = routes.pop()) != null) {
                    this.route(route, this.routes[route]);
                }
            },

            // Convert a route string into a regular expression, suitable for matching
            // against the current location hash.
            _routeToRegExp: function (route) {
                route = route.replace(escapeRegExp, '\\$&')
                    .replace(optionalParam, '(?:$1)?')
                    .replace(namedParam, function (match, optional) {
                        return optional ? match : '([^/?]+)';
                    })
                    .replace(splatParam, '([^?]*?)');
                return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
            },

            // Given a route, and a URL fragment that it matches, return the array of
            // extracted decoded parameters. Empty or unmatched parameters will be
            // treated as `null` to normalize cross-browser behavior.
            _extractParameters: function (route, fragment) {
                var params = route.exec(fragment).slice(1);
                return _.map(params, function (param, i) {
                    // Don't decode the search params.
                    if (i === params.length - 1) return param || null;
                    return param ? decodeURIComponent(param) : null;
                });
            }

        });

        // Backbone.History
        // ----------------

        // Handles cross-browser history management, based on either
        // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
        // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
        // and URL fragments. If the browser supports neither (old IE, natch),
        // falls back to polling.
        var History = Backbone.History = function () {
            this.handlers = [];
            _.bindAll(this, 'checkUrl');

            // Ensure that `History` can be used outside of the browser.
            if (typeof window !== 'undefined') {
                this.location = window.location;
                this.history = window.history;
            }
        };

        // Cached regex for stripping a leading hash/slash and trailing space.
        var routeStripper = /^[#\/]|\s+$/g;

        // Cached regex for stripping leading and trailing slashes.
        var rootStripper = /^\/+|\/+$/g;

        // Cached regex for stripping urls of hash.
        var pathStripper = /#.*$/;

        // Has the history handling already been started?
        History.started = false;

        // Set up all inheritable **Backbone.History** properties and methods.
        _.extend(History.prototype, Events, {

            // The default interval to poll for hash changes, if necessary, is
            // twenty times a second.
            interval: 50,

            // Are we at the app root?
            atRoot: function () {
                var path = this.location.pathname.replace(/[^\/]$/, '$&/');
                return path === this.root && !this.getSearch();
            },

            // In IE6, the hash fragment and search params are incorrect if the
            // fragment contains `?`.
            getSearch: function () {
                var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
                return match ? match[0] : '';
            },

            // Gets the true hash value. Cannot use location.hash directly due to bug
            // in Firefox where location.hash will always be decoded.
            getHash: function (window) {
                var match = (window || this).location.href.match(/#(.*)$/);
                return match ? match[1] : '';
            },

            // Get the pathname and search params, without the root.
            getPath: function () {
                var path = decodeURI(this.location.pathname + this.getSearch());
                var root = this.root.slice(0, -1);
                if (!path.indexOf(root)) path = path.slice(root.length);
                return path.charAt(0) === '/' ? path.slice(1) : path;
            },

            // Get the cross-browser normalized URL fragment from the path or hash.
            getFragment: function (fragment) {
                if (fragment == null) {
                    if (this._hasPushState || !this._wantsHashChange) {
                        fragment = this.getPath();
                    } else {
                        fragment = this.getHash();
                    }
                }
                return fragment.replace(routeStripper, '');
            },

            // Start the hash change handling, returning `true` if the current URL matches
            // an existing route, and `false` otherwise.
            start: function (options) {
                if (History.started) throw new Error('Backbone.history has already been started');
                History.started = true;

                // Figure out the initial configuration. Do we need an iframe?
                // Is pushState desired ... is it available?
                this.options = _.extend({root: '/'}, this.options, options);
                this.root = this.options.root;
                this._wantsHashChange = this.options.hashChange !== false;
                this._hasHashChange = 'onhashchange' in window;
                this._wantsPushState = !!this.options.pushState;
                this._hasPushState = !!(this.options.pushState && this.history && this.history.pushState);
                this.fragment = this.getFragment();

                // Normalize root to always include a leading and trailing slash.
                this.root = ('/' + this.root + '/').replace(rootStripper, '/');

                // Transition from hashChange to pushState or vice versa if both are
                // requested.
                if (this._wantsHashChange && this._wantsPushState) {

                    // If we've started off with a route from a `pushState`-enabled
                    // browser, but we're currently in a browser that doesn't support it...
                    if (!this._hasPushState && !this.atRoot()) {
                        var root = this.root.slice(0, -1) || '/';
                        this.location.replace(root + '#' + this.getPath());
                        // Return immediately as browser will do redirect to new url
                        return true;

                        // Or if we've started out with a hash-based route, but we're currently
                        // in a browser where it could be `pushState`-based instead...
                    } else if (this._hasPushState && this.atRoot()) {
                        this.navigate(this.getHash(), {replace: true});
                    }

                }

                // Proxy an iframe to handle location events if the browser doesn't
                // support the `hashchange` event, HTML5 history, or the user wants
                // `hashChange` but not `pushState`.
                if (!this._hasHashChange && this._wantsHashChange && (!this._wantsPushState || !this._hasPushState)) {
                    var iframe = document.createElement('iframe');
                    iframe.src = 'javascript:0';
                    iframe.style.display = 'none';
                    iframe.tabIndex = -1;
                    var body = document.body;
                    // Using `appendChild` will throw on IE < 9 if the document is not ready.
                    this.iframe = body.insertBefore(iframe, body.firstChild).contentWindow;
                    this.iframe.document.open().close();
                    this.iframe.location.hash = '#' + this.fragment;
                }

                // Add a cross-platform `addEventListener` shim for older browsers.
                var addEventListener = window.addEventListener || function (eventName, listener) {
                    return attachEvent('on' + eventName, listener);
                };

                // Depending on whether we're using pushState or hashes, and whether
                // 'onhashchange' is supported, determine how we check the URL state.
                if (this._hasPushState) {
                    addEventListener('popstate', this.checkUrl, false);
                } else if (this._wantsHashChange && this._hasHashChange && !this.iframe) {
                    addEventListener('hashchange', this.checkUrl, false);
                } else if (this._wantsHashChange) {
                    this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
                }

                if (!this.options.silent) return this.loadUrl();
            },

            // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
            // but possibly useful for unit testing Routers.
            stop: function () {
                // Add a cross-platform `removeEventListener` shim for older browsers.
                var removeEventListener = window.removeEventListener || function (eventName, listener) {
                    return detachEvent('on' + eventName, listener);
                };

                // Remove window listeners.
                if (this._hasPushState) {
                    removeEventListener('popstate', this.checkUrl, false);
                } else if (this._wantsHashChange && this._hasHashChange && !this.iframe) {
                    removeEventListener('hashchange', this.checkUrl, false);
                }

                // Clean up the iframe if necessary.
                if (this.iframe) {
                    document.body.removeChild(this.iframe.frameElement);
                    this.iframe = null;
                }

                // Some environments will throw when clearing an undefined interval.
                if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
                History.started = false;
            },

            // Add a route to be tested when the fragment changes. Routes added later
            // may override previous routes.
            route: function (route, callback) {
                this.handlers.unshift({route: route, callback: callback});
            },

            // Checks the current URL to see if it has changed, and if it has,
            // calls `loadUrl`, normalizing across the hidden iframe.
            checkUrl: function (e) {
                var current = this.getFragment();

                // If the user pressed the back button, the iframe's hash will have
                // changed and we should use that for comparison.
                if (current === this.fragment && this.iframe) {
                    current = this.getHash(this.iframe);
                }

                if (current === this.fragment) return false;
                if (this.iframe) this.navigate(current);
                this.loadUrl();
            },

            // Attempt to load the current URL fragment. If a route succeeds with a
            // match, returns `true`. If no defined routes matches the fragment,
            // returns `false`.
            loadUrl: function (fragment) {
                fragment = this.fragment = this.getFragment(fragment);
                return _.any(this.handlers, function (handler) {
                    if (handler.route.test(fragment)) {
                        handler.callback(fragment);
                        return true;
                    }
                });
            },

            // Save a fragment into the hash history, or replace the URL state if the
            // 'replace' option is passed. You are responsible for properly URL-encoding
            // the fragment in advance.
            //
            // The options object can contain `trigger: true` if you wish to have the
            // route callback be fired (not usually desirable), or `replace: true`, if
            // you wish to modify the current URL without adding an entry to the history.
            navigate: function (fragment, options) {
                if (!History.started) return false;
                if (!options || options === true) options = {trigger: !!options};

                // Normalize the fragment.
                fragment = this.getFragment(fragment || '');

                // Don't include a trailing slash on the root.
                var root = this.root;
                if (fragment === '' || fragment.charAt(0) === '?') {
                    root = root.slice(0, -1) || '/';
                }
                var url = root + fragment;

                // Strip the hash and decode for matching.
                fragment = decodeURI(fragment.replace(pathStripper, ''));

                if (this.fragment === fragment) return;
                this.fragment = fragment;

                // If pushState is available, we use it to set the fragment as a real URL.
                if (this._hasPushState) {
                    this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);

                    // If hash changes haven't been explicitly disabled, update the hash
                    // fragment to store history.
                } else if (this._wantsHashChange) {
                    this._updateHash(this.location, fragment, options.replace);
                    if (this.iframe && (fragment !== this.getHash(this.iframe))) {
                        // Opening and closing the iframe tricks IE7 and earlier to push a
                        // history entry on hash-tag change.  When replace is true, we don't
                        // want this.
                        if (!options.replace) this.iframe.document.open().close();
                        this._updateHash(this.iframe.location, fragment, options.replace);
                    }

                    // If you've told us that you explicitly don't want fallback hashchange-
                    // based history, then `navigate` becomes a page refresh.
                } else {
                    return this.location.assign(url);
                }
                if (options.trigger) return this.loadUrl(fragment);
            },

            // Update the hash location, either replacing the current entry, or adding
            // a new one to the browser history.
            _updateHash: function (location, fragment, replace) {
                if (replace) {
                    var href = location.href.replace(/(javascript:|#).*$/, '');
                    location.replace(href + '#' + fragment);
                } else {
                    // Some browsers require that `hash` contains a leading #.
                    location.hash = '#' + fragment;
                }
            }

        });

        // Create the default Backbone.history.
        Backbone.history = new History;

        // Helpers
        // -------

        // Helper function to correctly set up the prototype chain, for subclasses.
        // Similar to `goog.inherits`, but uses a hash of prototype properties and
        // class properties to be extended.
        var extend = function (protoProps, staticProps) {
            var parent = this;
            var child;

            // The constructor function for the new subclass is either defined by you
            // (the "constructor" property in your `extend` definition), or defaulted
            // by us to simply call the parent's constructor.
            if (protoProps && _.has(protoProps, 'constructor')) {
                child = protoProps.constructor;
            } else {
                child = function () {
                    return parent.apply(this, arguments);
                };
            }

            // Add static properties to the constructor function, if supplied.
            _.extend(child, parent, staticProps);

            // Set the prototype chain to inherit from `parent`, without calling
            // `parent`'s constructor function.
            var Surrogate = function () {
                this.constructor = child;
            };
            Surrogate.prototype = parent.prototype;
            child.prototype = new Surrogate;

            // Add prototype properties (instance properties) to the subclass,
            // if supplied.
            if (protoProps) _.extend(child.prototype, protoProps);

            // Set a convenience property in case the parent's prototype is needed
            // later.
            child.__super__ = parent.prototype;

            return child;
        };

        // Set up inheritance for the model, collection, router, view and history.
        Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;

        // Throw an error when a URL is needed, and none is supplied.
        var urlError = function () {
            throw new Error('A "url" property or function must be specified');
        };

        // Wrap an optional error callback with a fallback error event.
        var wrapError = function (model, options) {
            var error = options.error;
            options.error = function (resp) {
                if (error) error(model, resp, options);
                model.trigger('error', model, resp, options);
            };
        };

        return Backbone;

    }));

});